The genus Bordetella is the causative agent for a number of bacterial diseases, for example Bordetella pertussis (also known as Haemophilus pertussis) is responsible for whooping cough, a respiratory disease that can be severe in infants and young children. The clinical course of the disease is characterised by paroxysms of rapid coughs followed by inspiratory effort, often associated with a characteristic ‘whooping’ sound. In serious cases, oxygen deprivation can lead to brain damage; however the most common complication is secondary pneumonia.
Whooping cough is usually considered to be caused by B. pertussis, but occasionally B. parapertussis is isolated from patients with typical signs and symptoms of whooping cough. B. parapertussis infection is of lower frequency than B. pertussis with 5-10% of whooping cough being associated with B. parapertussis (Mertsola (1985) Eur J Clin Microbiol 4; 123; Lautrop (1971) Lancet 1(7711) 1195-1198). B. parapertussis is associated with mild clinical symptoms which, combined with its serological cross-reactivity with B. pertussis, makes B. parapertussis difficult to diagnose.
The first generation of vaccines against B. pertussis were whole cell vaccines, composed of whole killed bacteria. These were introduced in many countries in the 1950s and 1960s and were successful at reducing the incidence of whooping cough. A problem with whole cell B. pertussis vaccines is the high level of reactogenicity associated with them. Acellular vaccines containing purified B. pertussis proteins are less reactogenic and have been adopted for the vaccination programmes of many countries. Acellular vaccines typically containing pertussis toxin (PT), filamentous haemagglutinin (FHA) and quite often pertactin (PRN), are widely used and provide effective protection from the severity of whooping cough.
Bordetella toxins for use in such vaccines are generated by fermenting Bordetella and isolating the produced virulence factors, however Bordetella species are fastidious organisms which are difficult to grow in high concentrations (Doern Clin. infect. dis. 2000, 30 166-173), furthermore it is difficult to express Bordetella virulence factors such as FHA (filamentous haemagluttinin), Pertactin (PRN) and Pertusiss Toxin (PT) from Bordetella pertussis at high levels.
Bordetella can be grown in chemically defined media. For example Stainer and Scholte (Journal of General Microbiology (1971), 63, 211-220) discloses a simple chemically defined medium for the production of pertussis. Growth in chemically defined media provides advantages as undefined media can vary in their nutritional content leading to unpredictability in growth and expression.
However chemically defined medium can be expensive and difficult to manufacture in large amounts, in addition it is difficult to design balanced chemically defined media that support high levels of toxin production. The present inventors have surprisingly found that a number of modifications can be made to a chemically defined medium for a species of Bordetella pertussis to form simple media which support high levels of virulence factor production.